1. Field of the Invention
The present invention relates to multimetal oxide compositions of the formula I EQU [A].sub.p [B].sub.q (I),
where
A is Mo.sub.12 X.sup.1.sub.a X.sup.2.sub.b X.sup.3.sub.c X.sup.4.sub.d S.sub.e X.sup.5.sub.f O.sub.x PA1 B is X.sup.6.sub.12 X.sup.7.sub.g X.sup.8.sub.h O.sub.y PA1 Mo: ammonium heptamolybdate, PA1 Fe: iron nitrate (aqueous solution), PA1 Co: cobalt nitrate (aqueous solution), PA1 Alkali metal: alkali metal nitrate, PA1 Rh: rhodium chloride, PA1 Re: rhenium pentoxide or ammonium perrhenate. PA1 Mo: ammonium heptamolybdate, PA1 V: ammonium metavanadate, PA1 P: from 70 to 100%, preferably from 76 to 85%, strength by weight phosphoric acid, PA1 Sb: senarmontite, PA1 S: ammonium sulfate, PA1 Re: rhenium pentoxide or ammonium perrhenate, PA1 B: boric acid, PA1 As: arsenic trioxide, PA1 Si: waterglass, PA1 Nb: ammonium niobium oxalate or ammonium niobate, PA1 Alkali metals: alkali metal nitrates, PA1 NH.sub.4 : ammonium sulfate, nitrate or carbonate, PA1 Bi: bismuth nitrate.
X.sup.1 is phosphorus, arsenic, boron, germanium and/or silicon,
X.sup.2 is vanadium, niobium and/or tungsten,
X.sup.3 is hydrogen, of which up to 97 mol % may have been replaced by potassium, rubidium, cesium and/or ammonium (NH.sub.4),
X.sup.4 is antimony and/or bismuth,
X.sup.5 is rhenium and/or rhodium,
X.sup.6 is molybdenum, tungsten, niobium and/or tantalum,
X.sup.7 is iron, cobalt, nickel, rhodium, ruthenium, magnesium, calcium, strontium, barium, zinc, cadmium, mercury, yttrium, scandium and/or a rare-earth metal, where, of the latter, cerium, lanthanum and europium are preferred,
X.sup.8 is lithium, sodium, potassium, rubidium, cesium and/or ammonium (NH.sub.4),
a is from 1 to 6, preferably from 1 to 3, particularly preferably from 1.5 to 2.5
b is from 0 to 6, preferably from 0.2 to 4, particularly preferably from 0.5 to 2
c is from 3 to 5,
d is from 0 to 6, preferably from 0 to 3, particularly preferably from 0.5 to 1.5
e is from 0 to 3, preferably from 0.01 to 1, particularly preferably from 0.01 to 0.2,
f is from 0 to 3, preferably from 0.01 to 1, particularly preferably from 0.01 to 0.5,
g is from 0.5 to 20, preferably from 4 to 15, particularly preferably from 6 to 12,
h is from 0 to 4, preferably from 0.01 to 3, particularly preferably from 0.01 to 2,
x and y are numbers determined by the valency and frequency of the elements other than oxygen in I, and
p and q are numbers other than zero whose ratio p/q is from 12:0.1 to 12:48, preferably from 12:0.25 to 12:12, particularly preferably from 12:0.5 to 12:4,
which contain component [A].sub.p in the form of three-dimensionally extended regions A of the chemical composition EQU Mo.sub.12 X.sup.1.sub.a X.sup.2.sub.b X.sup.3.sub.c X.sup.4.sub.d S.sub.e X.sup.5.sub.f O.sub.x A
which are delimited from their local environment due to their chemical composition which is different from their local environment, and component [B].sub.q in the form of three-dimensionally extended regions B of the chemical composition EQU X.sup.6.sub.12 X.sup.7.sub.g X.sup.8.sub.h O.sub.y B
which are delimited from their local environment due to their chemical composition which is different from their local environment, where the regions A and B are distributed relative to one another as in a finely divided mixture of A and B.
The present invention also relates to a process for the preparation of these compositions, and to their use.
2. Discussion of the Background
DE-A 26 10 249 and EP-A 180 997 relate to multimetal oxide compositions whose empirical elemental composition corresponds to that of the novel multimetal oxide compositions.
These multimetal oxide compositions are prepared by converting suitable sources of the constituents of the desired multimetal oxide compositions in the requisite amounts into an intimate dry mix, and subsequently calcining the latter at elevated temperature for several hours. The resultant multimetal oxide compositions are recommended, inter alia, as catalysts for the preparation of methacrylic acid from methacrolein by gas-phase catalytic oxidation. However, the multimetal oxide compositions of this prior art have the disadvantage that both their activity and the selectivity in the formation of methacrylic acid for a given conversion are not entirely satisfactory. The same applies to the reproducibility of their preparation and to their service lives, which are particularly unsatisfactory if the reaction gases comprising methacrolein as the principal constituent contain organic acids as secondary constituents.